Blast diffuser

ABSTRACT

A blast diffuser for a gun, comprising bore means having a surface defining a barrel through which a projectile may be discharged when a diffuser is attached, in use, to a gun barrel, the blast diffuser further comprising primary chamber arranged around the outside of the bore means and a secondary chamber adjacent to an outer surface of the primary chamber, wherein a plurality of holes are arranged in the surface of the bore means to the primary chamber, and a plurality of holes are arranged in the outer surface of the primary chamber to allow passage of combustion gasses from the primary chamber further comprising an opening to allow the escape of combustion gasses into the atmosphere.

FIELD OF THE INVENTION

[0001] The invention relates to a blast diffuser for reducing the soundpressure level caused by the high-pressure combustion gases generated bythe firing of a gun. Although the description relates to the use of theblast diffuser to reduce the blast pressure from a mortar gun ofpreferably 120 mm calibre, it should be appreciated that the inventionmay be applied to guns with other calibres with suitable modifications.

BACKGROUND AND PRIOR ART

[0002] During the firing of large calibre guns, the combustion gases andpressure waves generated by the blast of the gun can be considerable. Asa result, especially for guns of 120 mm calibre or greater, the operatorof the gun has to station himself at a safe distance from the blast areato avoid injuries that may be caused by such pressure levels. In thecase of muzzle-loaded weapons, such as mortars, the problem is moreacute as it is necessary for the operator to be in relatively closeproximity to the barrel in order to operate the weapon effectively,

[0003] Due to a desire to increase the rate of fire of a mortar gun, thepeak sound pressure level at the operator's position when firing themortar artillery system would tend to exceed the safety limit of the “Zline zone” as defined in the military standardization specificationsMIL-STD 1474C (“Noise limits for military material”). This problem hasconstrained the firepower of the mortar system as it limits the totalnumber of rounds that can be safely fired per day by an operator.

[0004] Conventionally, this problem may be resolved by remotelytriggering the mortar firing. However, the rate of fire will besignificantly reduced. The problem is accentuated by the development ofmodern mortar systems that are designed for high rates of fire withsemi-automatic bomb loading systems.

[0005] There are various devices that have been developed to attenuatethe sound pressure levels generated by the firing of a gun. A majorityof these devices seek to divert the propellant gases leaving the gunbarrel so that they may be allowed to expand or cool inside a chamber,or by drawing the propellant gases out of the barrel in a controlledmanner. An example is U.S. Pat. No. 5,610,360 for a “Large Caliber GunMuffler”. The patent describes a muffler for a large calibre gun havinga gun tube that includes a transition section fitted around the gun tubeand engaging the gun tube for preventing the escape of residualcombustion gases caused by the firing of a projectile by the gun. Thetransition section further includes a pressure vessel, vent stack, valveand exhaust blower to draw propellant gases out of the gun tube.

[0006] The device described in the patent is elaborate and contains manyparts. It also includes external attachments such as an exhaust blowerwhich increases the complexity of the operation. Whilst it may beworkable in a gun-testing environment, it is not practical for fieldcombat operations because of its complexity and bulk, that would add tothe operational overheads.

SUMMARY OF THE INVENTION

[0007] It is thus an objective of the present invention to provide animproved blast diffuser to reduce the sound pressure levels affectingthe operators of guns, especially large calibre guns.

[0008] One aspect of the present invention provides a blast diffuser fora gun, comprising bore means having a surface defining a barrel throughwhich a projectile may be discharged when the diffuser is attached, inuse to a gun barrel, the blast diffuser further comprising a primarychamber arranged around the outside of the bore means and a secondarychamber adjacent to an outer surface of the primary chamber, wherein aplurality of holes are arranged in the surface of the bore means toallow the passage of combustion gases from the bore means to the primarychamber, and a plurality of holes are arranged in he outer surface ofthe primary chamber to allow the passage of combustion gases from theprimary chamber to the secondary chamber, the secondary chamber furthercomprising an opening to allow the escape of combustion gases into theatmosphere.

[0009] Another aspect of the invention provides a gun having a blastdiffuser, the gun comprising a gun barrel, a primary chamber arrangedaround the outside of the gun barrel and a secondary chamber adjacent toan outer surface of the primary chamber, wherein a plurality of holesare arranged in the surface of the gun barrel to allow the passage ofcombustion gases from the gun barrel to the primary chamber, and aplurality of holes are arranged in the outer surface of the primarychamber to allow the passage of combustion gases from the primarychamber to the secondary chamber, the secondary camber furthercomprising an opening to allow the escape of combustion gases into theatmosphere.

[0010] It will be convenient to hereinafter describe an embodiment ofthe present invention with reference to the accompanying drawings whichillustrate one form of diffuser incorporating the invention. It is to beunderstood that the particularity of the drawings and the relateddescription is not to be understood as superseding the generality of thebroad description of the invention as defined in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is an isometric view of a blast diffuser according to apreferred embodiment of the invention.

[0012]FIG. 2 is a cross-sectional view of the blast diffuser along lineC-C of FIG. 1.

[0013]FIG. 3 is a plan view of the blast diffuser of FIG. 1.

[0014]FIG. 4 is a sectional view of the blast diffuser along line Y-Y ofFIG. 3 showing the outer holes and dispersion plates in more detail.

[0015]FIG. 5 comprises tables 1 and 2 giving test results relating tothe use of the blast diffuser to fire charge 8 and charge 9 bombs for amortar gun.

[0016]FIG. 6 is a graph showing the test-firing results at a positionone meter from the barrel muzzle using a charge 8 round according toMIL-STD-1474C.

[0017]FIG. 7 is a graph showing the test-firing results at a positionone meter from the barrel muzzle using a charge 9 round according toMIL-STD-1474C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

[0018]FIG. 1 is an isometric view of a blast diffuser 10 according to apreferred embodiment of the invention. In the preferred embodiment, theblast diffuser 10 is adapted to be fitted onto the muzzle of a barrel ofa mortar gun (indicated by numeral 11 in FIG. 2). The blast diffuser 10comprises of a muzzle adapter 12, a diffuser barrel 14 and an opening 16for the discharge of a projectile. Alternatively, the blast diffuser 10may form a part of the barrel of the mortar gun itself, in, which casethe diffuser barrel 14 comprises a portion of the barrel of the mortargun.

[0019] Adjacent to the diffuser barrel 14 are affixed attenuationattachments 18 on opposite sides of the diffuser barrel 14 consisting ofprimary chambers 20 connected to the diffuser barrel 14 and secondarychambers 22 connected to the primary chambers 20. It would beappreciated that during firing of a mortar bomb, the bomb projectilewould travel past the muzzle adapter 12, diffuser barrel 14 and bedischarged through the opening 16.

[0020]FIG. 2 is a cross-sectional view of the blast diffuser 10 alongline C-C of FIG. 1. Along the surface of the diffuser barrel 14 betweenthe diffuser barrel 14 and the primary chamber 20, there are a pluralityof inner holes 24 that allow the escape of combustion gases from thediffuser barrel 14 to the primary chamber 20. The aim is to deflect thegases through an outlet in a direction substantially transverse to thetrajectory of the projectile.

[0021] As illustrated in FIG. 2, the top and bottom of the primarychamber 20 are sealed, allowing the escape of combustion from theprimary chamber 20 to the secondary chamber 22 only through the outerholes 26 found on the surface separating the primary chamber 20 and thesecondary chamber 22. The secondary chamber 22 has a secondary chamberopening 28 at its top to allow escape of gases into the atmosphere. Thebottom of the secondary chamber 22 is sealed.

[0022] During firing, a projectile (not shown) is propelled byhigh-pressure combustion gases. As the projectile passes through theblast diffuser 10, some of the gases will escape through the inner holes24 of the diffuser barrel 14. These gases will expand into the primarychambers 20. Thereafter, these gases will escape through the outer holes26 and further expand into the secondary chambers 22. The gases willthen be discharged through the secondary chamber opening 28. Therefore,the gas pressure will be significantly reduced before the projectileleaves the barrel. Hence, the peak sound pressure level at theoperator's position is also significantly reduced.

[0023] In addition, there are a series of deflection plates 30interspersed in the secondary chambers 22 along the surface of thesecondary chambers 22 next to the outer holes 26. The deflection plates30 prevent smooth flow of the high-pressure gases to the secondarychamber openings 28 and thus further reduces the energy possessed by thegases before discharge into the atmosphere.

[0024] The blast diffuser will serve to reduce the peak sound pressurelevel at the operator's position to a safer level when firinglarge-calibre artillery systems. The improvement will assistsubstantially in the operation of modern artillery systems that aredesigned for high rates of fire and semi-automatic operation, inparticular mortar systems.

[0025]FIG. 3 is a plan view of the blast diffuser 10 of FIG. 1. It showsthe orientation of the primary chambers 20 and secondary chambers 22relative to the diffuser barrel 14, as well as the secondary chamberopening 28 of the secondary chamber 22.

[0026]FIG. 4 is a sectional view of the blast diffuser along line Y-Y ofFIG. 3 showing the outer holes and dispersion plates in more detail. Thearrows illustrate the air-flow that is deflected by the deflectionplates 30 to prevent smooth flow of the high-pressure gases to thesecondary chambers openings 28 to further reduce the energy possessed bythe gases before discharge into the atmosphere.

[0027] The test results of the blast diffuser that were conducted inaccordance with MIL-STD-1474C are tabulated in Tables 1 & 2 of FIG. 5.The results show that the blast diffuser is able to reduce peak soundpressure level at one meter away from the barrel muzzle by 184% inpressure or 9.0 dB when firing charge 8 bombs and to reduce the peaksound pressure level by 167% in pressure or 8.6 dB when firing charge 9bombs. Both these results bring the sound pressure levels to below the“Z line zone” as defined in the MIL-STD 1474C.

[0028]FIGS. 6 and 7 are graphs showing the test-firing results at aposition one meter from the barrel muzzle using charge 8 and charge 9rounds respectively according to MIL-STD-1474C. The “Z line zone” isrepresented by the area above PPLz. From the graphs, it is clear thatbarrel muzzles fitted with the blast diffuser according to the presentinvention are able to attain peak sound pressure levels at below the “Zline zone”.

[0029] While a particular embodiment of the invention has been shown anddescribed, it will be appreciated by those skilled in the art thatchanges and modifications of the present invention may be made withoutdeparting from the invention in broadest aspects. As such, the scope ofthe invention should not be limited by the particular embodiment andspecific construction described herein but should be defined by theappended claims and equivalents thereof. Accordingly, the aim in theappended claims is to cover all such changes and modifications as fallwithin the spirit and scope of the invention.

1. A blast diffuser for a gun, comprising bore means having a surfacedefining a barrel through which a projectile may be discharged when thediffuser is attached, in use, to a gun barrel, the blast diffuserfurther comprising a primary chamber arranged around the outside of thebore means and a secondary chamber adjacent to an outer surface of theprimary chamber, wherein a plurality of holes are arranged in thesurface of the bore means to allow the passage of combustion gases fromthe bore means to the primary chamber, and a plurality of holes arearranged in the outer surface of the primary chamber to allow thepassage of combustion gases from the primary chamber to the secondarychamber, the secondary chamber further comprising an opening to allowthe escape of combustion gases into the atmosphere.
 2. A blast diffuseraccording to claim 1, wherein the primary and secondary chambers arearranged radially with respect to the bore means.
 3. A blast diffuseraccording to claim 1 or 2, wherein the bore means and primary chamberare arranged so that the passage of gases into the primary chamber is ina direction substantially transverse to the axis of the bore means.
 4. Ablast diffuser according to any preceding claim, wherein deflectionmeans are provided in at least the secondary chamber for preventingsmooth flow of the combustion gases.
 5. A blast diffuser according claim4, wherein the deflection means comprise one or more deflection plates.6. A blast diffuser according to claim 5, wherein the deflection platesare provided along the surface of the secondary chamber adjacent to theholes between the primary and secondary chambers.
 7. A blast diffuseraccording to any preceding claim, comprising a plurality of primary andsecondary chambers.
 8. A blast diffuser according to claim 7, comprisingtwo attenuation portions arranged on diametrically opposite sides of thebore means, each attenuation portion comprising a primary chamber and asecondary chamber.
 9. A blast diffuser according to any preceding claim,wherein the opening in the or each secondary chamber is arranged so thatcombustion gases escape to the atmosphere in substantially the directionin which the gun is arranged to discharge a projectile.
 10. A blastdiffuser according to any preceding claim, further comprising a muzzleadapter at one end of the bore means for enabling attachment of thediffuser to the muzzle of a gun.
 11. A gun having a blast diffuser, thegun comprising a gun barrel, a primary chamber arranged around theoutside of the gun barrel and a secondary chamber adjacent to an outersurface of the primary chamber, wherein a plurality of holes arearranged in the surface of the gun barrel to allow the passage ofcombustion gases from the gun barrel to the primary chamber, and aplurality of holes are arranged in the outer surface of the primarychamber to allow the passage of combustion gases from the primarychamber to the secondary chamber, the secondary chamber furthercomprising an opening to allow the escape of combustion gases into theatmosphere.